1. Technical Field
The present invention relates generally to the handling of bulk materials, such as coal, grain, etc., for shipping purposes. More particularly, the present invention relates to an improved method and apparatus for adapting gantry-supported container loading facilities to handle such bulk materials.
2. Prior Art
Bulk materials, such as coal, grain, etc., are loaded into the holds of ships primarily with the use of conveyors which are snaked through the hold to deliver the material to the proper location. The conveyor equipment is expensive, requires a considerable amount of time to set up for use and is complex to handle. It would be far more convenient to load bulk material with the use of standard cargo containers of the type which are hoisted and positioned by means of a container spreader suspended from a gantry cantilever crane. The advantages which would accrue to the use of such containers by handling bulk materials are numerous. For example, cargo containers of bulk material could be transported to and from shipping ports by a wide variety of transport modes, such as flat-bed rail cars, substantially all trucks, etc., whereas loose bulk material is limited to vehicles which are specially designed for that purpose. In addition, containerized bulk material does not pollute the environment and is less susceptible to accidental explosions which Would result from loose dust in the air; the dust, of course, is retained within the container when the bulk material is containerized. Whereas loose bulk material leaves a dust or powder which renders the ship's hold unusable for transporting other products for a return trip, containerization of the material avoids this problem. Moreover, containerization permits much more precise positioning of the material within the hold as compared to conveying bulk material in loose form into the hold. Containerization also provides weather protection for the bulk material; this is extremely important in the case of coal, which when exposed to rain, forms sulfuric acid. Further, coal, grain, and other bulk products, when containerized, can be transported from any port having container-handling facilities; presently, these materials can only be transported from a port having special bulk material handling facilities. Containerized bulk material can be readily stored in transit to a shipping port without tying up the shipping vehicle, whereas loose bulk material can be readily stored in transit only in the specially provided railroad cars, etc.
Considering all of the aforementioned advantages of handling bulk material in cargo containers, one might wonder why this has not been the standard mode of shipping bulk material in the past. The reason lies in the fact that, until the present invention, there has been no practical technique for removing the bulk material from the containers at the destination port. Cargo containers are conventionally hoisted and positioned by means of container spreaders which are suspended from gantry cantilever cranes. Such cranes have no capability for tipping the containers to pour out the container contents. Attempts have been made in the past to tip such containers from a ground-supported position about a bottom edge of the container; however, the tipping action was not easily controlled and the side walls of the standard cargo containers tended to buckle from the weight of the material during tipping. The absence of tipping control was due primarily to the fact that the tipping axis was the bottom edge of the container rather than an axis passing through, or substantially through, the container center of gravity. As a consequence, the force required to pivot the container varies considerably at different positions during the tipping operation.